This invention relates to a velocity detection apparatus for elevators.
In the velocity control of elevators, there has recently been developed a system wherein the velocity of the cage of the elevator or the rotating velocity of the hoist motor thereof is digitally detected and is employed as a velocity feedback signal.
This system detects the velocity by generating movement magnitude pulses, which correspond to the magnitude of movement and direction of movement of the cage or the rotational angle and rotational direction of the hoist motor, and counting them at predetermined intervals. An apparatus for generating the movement magnitude pulses is disclosed in, for example, Japanese Laid-Open Patent Application No. 57-72582 (U.S. Pat. No. 4,446,946). The movement magnitude pulses in this system are, in general, derived from a disc which is rotated in direct coupling with the driving sheave of a hoisting machine or the sheave of a speed governor or through the medium of a transmission mechanism such as a pulley. They can also be derived from a disc which is rotated by a block around which a steel tape or the like coupled to the cage is wound. The disc is provided with apertures which are formed at equal intervals in the circumferential part thereof, and pulses at a frequency proportional to the rotational speed of the disc are produced by detecting the apertures optically or electromagnetically.
In the velocity control of an elevator, when employing movement magnitude pulses for the determination of a deceleration position and the positional feedback control of a velocity command in a deceleration region, the distance detection unit of the pulses may be on the order of several mm. When employing them for velocity feedback control, however, the speed of velocity detection becomes a problem with the above system wherein the movement magnitude pulses arriving within the predetermined period of time are counted to detect the velocity. The counting time intervals need to be shortened, and the distance detection unit of the movement magnitude pulses must be lowered by one to two orders. Moreover, in a low velocity region, the number of movement magnitude pulses arriving within a unit time decreases, and the distance detection unit of the movement magnitude pulses needs to be further lowered.
A movement magnitude pulse generator for fulfilling such conditions requires high mechanical precision which often involves high construction costs and therefore is not practical. At present, accordingly, a method is adopted in which the distance detection precision per pulse is enhanced by the mechanical means of speed-up coupling using gears or a pulley. The whole apparatus, however, also becomes very expensive.